1. Technical Field
This invention relates to metallic contacts used in wireless transceivers such as cordless telephones and, more particularly, to metallic contacts which provide protection from Electro-Static Discharge (ESD) for circuitry accessible through the contacts.
2. Description of the Prior Art
Wireless transceivers such as cordless telephones have been available in the art for a number of years. These transceivers typically comprise a fixed or base unit and an associated portable or handset unit. Initialization for subsequent communications between the base unit and the handset unit is achieved by placing the handset unit in a mating cradle in the base unit at which time metallic contacts on the base unit and the handset unit are mated together. Through these contacts, the base unit typically transfers a digital security code and a frequency channel assignment upon which the base unit and handset unit establish initial communications. Also, charging current from the base unit is provided through these metallic contacts to the handset unit for charging a battery which is located in the handset unit and provides operating power for this unit. Such operation is described in U.S. Pat. No. 4,736,404 which issued to R. E. Anglikowski et al. on Apr. 5, 1988.
As described in U.S. Pat. No. 4,736,404, the digital security code and frequency channel information are obtained from a microprocessor in the base unit and coupled via the metallic contacts to a microprocessor in the handset unit over a direct-current charging path that is established between these two units. This direct-current charging path exists between the base unit and the handset unit whenever the handset unit is nested in the cradle of the base unit. As long as the handset unit remains in the cradle of the base unit and the handset unit battery needs charging, charging current for this battery is generated in the base unit and this current is passed through the metallic contacts on the base unit and the metallic contacts on the handset unit to the battery in the handset unit.
When the handset unit is removed from the cradle of the base unit, the metallic contacts on both the base unit and the handset unit are exposed and a person is able to touch the contacts on these units. If that person happens to be electrically charged with static electricity and touches the metallic contacts, unfortunately, the electrical potential then held by that person may be discharged directly into ESD-sensitive circuitry, such as the microprocessor and/or other circuitry, which is connected to the touched metallic contact. Such electrical potential, when received by the microprocessor and other circuitry, could possibly cause the affected unit to malfunction. It is therefore desirable to isolate the metallic contacts from the ESD-sensitive circuitry when the handset unit is removed and located remote from the base unit.